As a type of a substrate processing apparatus, a batch type substrate processing apparatus includes a vertical-type reaction furnace, a boat that is a substrate retaining mechanism configured to retain a predetermined number of substrates to be processed (hereinafter referred to as ‘wafers’) such that the wafers are retained in a horizontal posture and a multistage manner, and a substrate transfer machine configured to transfer the wafers into the boat, and processes the wafers in the reaction furnace while the wafers are retained in the boat.
Conventionally, a wafer crack detecting mechanism is installed in a substrate processing apparatus to detect a defect occurring in a wafer, so that substrate processing may be prevented from being continuously performed when a defect (e.g., bending, a crack, or misalignment) occurs in the wafer due to a thermal stress caused by a temperature rise in the reaction furnace or a cooling process when the wafer is unloaded from the reaction furnace.
The wafer crack detecting mechanism includes a photo sensor, and detects the presence or absence of a wafer, a wafer crack, or wafer dropping in each of slots based on a waveform indicating an increase/decrease in the amount of light obtained by vertically adjusting an optical axis with respect to which the photo sensor radiates light in a horizontal direction in a manner that the radiated light is directed to a position of the wafer retained in the boat located about 5 mm to 10 mm toward a center of the wafer from a circumference of the wafer.
When a wafer is retained normally, the amount of light decreases starting from a lower part of the wafer and returns to its original level at an upper part of the wafer, and the state of the wafer is determined according to whether the amount of light falls within a reference level. When a matter other than the wafer is present in a region in which the optical axis and the wafer overlap, the matter is reflected in the waveform of the amount of light and it is thus determined that the wafer is in an abnormal state.
A substrate processing apparatus may be manufactured such that a ring-type retaining member is mounted on a boat and a wafer is placed on the retaining member so as to improve process performance conditions. However, if the retaining member is mounted on the boat, the retaining member may be present on an optical axis of the wafer crack detecting mechanism and a waveform of the amount of light may thus be influenced by the retaining member. Thus, the wafer crack detecting mechanism cannot be used in this case.
Furthermore, in this case, substrate processing is performed in a state in which the retaining member is mounted on the boat. In this case, deformation or misalignment of the retaining member may occur due to heat. Accordingly, there is a need to develop a mechanism capable of detecting whether deformation or misalignment occurs in the retaining member beforehand.